There have been well known noise suppressing technologies for, through processing of a mixed signal in which a first signal and a second signal are mixed, suppressing the second signal to output an emphasized signal (a signal resulting from emphasizing a desired signal). For example, a noise suppressor is a system for suppressing noise which is superposed on a desired speech signal. Such a noise suppressor is used in various audio terminals, such as a mobile telephone.
With respect to this kind of technology, in patent literature (PTL) 1, there is disclosed a method of suppressing noise by multiplying amplitude spectrum components of an input noisy speech signal by corresponding spectral gains each having a value smaller than or equal to “1”. Further, in PTL 2, there is disclosed a method of suppressing noise by directly subtracting spectrum components of estimated noise from corresponding spectrum components of a noisy speech signal.